1/1x3+1/2x4+1/3x5+1/4x6=1/5x7=1/6x8

如题所述

题目应是
1/1x3+1/2x4+1/3x5+1/4x6+1/5x7+1/6x8
=1/1x3+1/3x5+1/5x7+1/2x4+1/4x6+1/6x8
=2(1-1/3+1/3-1/5+1/5-1/7)+2(1/2-1/4+1/4-1/6+1/6-1/8)
=2(1-1/7+1/2-1/8)
=69/28

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